Teachers in the Neshaminy School District will go on strike Monday for the second time this year, their union announced Thursday, canceling classes and extending the school year.

“We told the district that the June 4 strike could be averted if they had an attitude adjustment and agreed to negotiate throughout the weekend, and they flatly rejected our offer,” said Louise Boyd, president of the Neshaminy Federation of Teachers, in a written statement.

The district rejected weekend talks because “they wouldn’t get us anywhere,” school board President Ritchie Webb said Friday. He cited union negotiators’ “insults, innuendo, and useless platitudes” at Thursday’s closed negotiating session with two state mediators.

The district and the union have been locked in a bitter contract dispute for four years – the longest current impasse in the state. The union’s 633 teachers, guidance counselors, librarians and nurses have not received a raise since 2008, working under the terms of the expired contract.

The strike, like the eight-day walkout in January, will cancel classes for the district’s 7,000 students. High school seniors, who were scheduled to take final exams next week, will be exempt from each test missed because of the strike, according to the district’s website. Their June 13 graduation will proceed as scheduled, according to the website.

By state law, the 180-day school year must be completed by June 30, without weekend classes. That means teachers could stay out about 10 days.

The union notified the district on May 25 that it might strike Monday, depending on Thursday’s negotiating session, which both sides characterized as unproductive. The talks had been suspended since December because of the strike and a state-required arbitration that followed.

The findings from the nonbinding arbitration, issued last month, would cost the district $20 million for items including retroactive pay and continued bonuses for early retirement, Webb said. The school board uanimously rejected the findings, while union members approved them “with reservations.”

The next negotiating session is scheduled for June 12, but it will be canceled if teachers are on strike, Webb said.

Before Thursday’s session at Maple Point Middle School, about 55 residents -- including a handful of students -- held signs to show their support for the school board and opposition to the union’s tactics.

“This is really to show the NFT that they don’t have the upper hand,” said Michele Fay, one of the organizers of the demonstration. “They should just leave our kids out of it.”

After the January strike, Fay’s son, an honors student, told her he was struggling with his 10th-grade classes, she said.

"He has a 3.65 GPA,” Fay said, “and I don’t want the strike to affect it.”

Sue Hoch, another organizer, said the impasse has dragged on so long that “we don’t know what to do any more. This is all we have left.”